-----Original Message-----
From: Bill William <iodideshi@yahoo.co.jp>
Sent: Aug 23, 2004 9:29 PM
To: alt-photo-process-l@sask.usask.ca
Subject: physical developers
Speaking of physical developers, anyone here use them?
Got any formulas / experience you would like to share?
Ray
__________________________________________________
I have no direct experience but will refer you to Richard Henry's famous book _Controls in Black and White Photography, second edition. This has gotten quite rare but some libraries may have it. In it Dr. Henry reports on some controlled tests using the O'dell formulas. His conclusions are that the claims made for it are not borne out in practice. Haist has a short section on physical developers in _Modern Photographic Processing_. For those not familiar with the term a physical developer is one that plates silver onto the development centers of the exposed halide particals rather than converting the halide to silver, a process known as chemical development. It is likely that some fine grain chemical developers have some contribution from solution physical development.
If a plain fixing bath is used it is actually possible to develop the latent image in fixed out film by means of a physical developer. This is mostly of academic interest but it is a demonstration of how the development specks produced by light remain in the gelatin even when the silver halide is removed. The sensitivity of the film is very much reduced, perhaps on the order of ten or twenty times when this process is used. I am away from my references now so am going on memory but I think this is correct at least as to order of magnitude.
Again, from what Dr. Henry found physical development has no advantages in practice. Although it is claimed ot produce extremely fine grain Henry found that it was no finer, and sometimes coarser, than D-76.
It would probably be intresting to experiment with.
Richard Knoppow
dickburk@ix.netcom.com
Los Angeles, CA, USA
Received on Mon Aug 23 23:51:28 2004
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